Image sensors and methods of forming the same

ABSTRACT

An image sensor includes a substrate including a plurality of pixel regions and having a trench between the pixel regions, a photoelectric conversion part in the substrate of each of the pixel regions, and a device isolation pattern in the trench. The device isolation pattern defines an air gap. The device isolation pattern has an intermediate portion and an upper portion narrower than the intermediate portion.

CROSS-REFERENCE TO RELATED APPLICATION

This U.S. non-provisional patent application is a Divisional of U.S.application Ser. No. 14/994,230, filed Jan. 13, 2016, which claimspriority under 35 U.S.C. § 119 to Korean Patent Application No.10-2015-0006012, filed on Jan. 13, 2015, in the Korean IntellectualProperty Office, the entire content of each of which is incorporated byreference in its entirety.

BACKGROUND 1. Field

Some example embodiments of the inventive concepts relate to imagesensors including device isolation patterns and/or methods of formingthe same.

2. Description of the Related Art

An image sensor is a semiconductor device that converts an optical imageinto electrical signals. Image sensors may be categorized as any one ofcharge coupled device (CCD)-type image sensors and complementarymetal-oxide-semiconductor (CMOS)-type image sensors. CIS is short forthe CMOS-type image sensor. The CIS may include a plurality of pixelstwo-dimensionally arranged, and each of the pixels may include aphotodiode (PD). The photodiode may convert incident light into anelectrical signal.

As semiconductor devices have been highly integrated, image sensors havealso been highly integrated. Sizes of pixels have been reduced by thehigh integration density of the image sensor, so crosstalk may occurbetween the pixels.

SUMMARY

Some example embodiments of the inventive concepts may provide imagesensors capable of reducing or minimizing crosstalk between pixels andmethods of forming the same.

According to an example embodiment, an image sensor includes a substrateincluding a plurality of pixel regions and having a trench between thepixel regions, a photoelectric conversion part in each of the pixelregions, and a device isolation pattern in the trench. The deviceisolation pattern defines an air gap. An upper portion of the deviceisolation pattern is narrower than an intermediate portion of the deviceisolation pattern.

In an example embodiment, the device isolation pattern may furtherinclude an insulating layer on a first surface of the substrate. Anupper portion of the trench may be delimited by the insulating layer.

In an example embodiment, the insulating layer may extend along a bottomsurface and sidewalls of the trench.

In an example embodiment, a top surface of the insulating layer on thebottom surface of the trench may be spaced apart from a bottom surfaceof the insulating layer delimiting the upper portion of the trench.

In an example embodiment, a thickness of the insulating layer on thefirst surface of the substrate may be equal to that of the insulatinglayer on the bottom surface and the sidewalls of the trench.

In an example embodiment, a width of a bottom portion of the deviceisolation pattern may be narrower than a width of the intermediateportion of the device isolation pattern.

In an example embodiment, sidewalls of the device isolation pattern maybe coplanar with sidewalls of the trench.

According to another example embodiment, an image sensor includes asubstrate including a plurality of pixel regions, a device isolationpattern in the substrate and on a first surface of the substrate todefine the pixel regions, and a photoelectric conversion part providedin each of the pixel regions. The device isolation pattern defines anair gap. An upper portion of the device isolation pattern is adjacent tothe first surface of the substrate, and the upper portion of the deviceisolation pattern has an increasing width at an increasing distance fromthe first surface of the substrate.

In another example embodiment, the device isolation pattern may furtherinclude an insulating layer covering the first surface of the substrate.The upper portion of the device isolation pattern may be delimited bythe insulating layer.

In another example embodiment, the insulating layer may also extendalong sidewalls and a bottom surface of the device isolation pattern.

In another example embodiment, a refractive index of the insulatinglayer may be lower than that of the substrate and may be higher thanthat of the air gap.

In another example embodiment, a lower portion of the device isolationpattern may have a decreasing width at a decreasing distance from abottom surface of the device isolation pattern.

In another example embodiment, the image sensor may further includecolor filters on the first surface of the substrate, a transfer gate ineach of the pixel regions on a second surface of the substrate, and aninterconnection structure on the second surface of the substrate tocover the transfer gate in each of the pixel regions.

According to still another example embodiment, a method of forming animage sensor includes forming a trench in a substrate, and forming aninsulating layer on a first surface of the substrate delimiting theupper portion of the trench to form a device isolation pattern definingan air gap. An upper portion of the trench is narrower than anintermediate portion of the trench, and the device isolation patterndefines pixel regions in the substrate.

In still another example embodiment, forming the trench may includeforming a mask pattern having an opening with a first width on the firstsurface of the substrate, and etching the substrate exposed by the maskpattern. The upper portion of the trench may have a width equal to orgreater than the first width.

In still another example embodiment, etching the substrate may includeisotropically etching the substrate using an etching gas containingfluorine.

In still another example embodiment, the trench may extend under themask pattern in the substrate.

In still another example embodiment, the upper portion of the trench mayhave an increasing width at an increasing distance from the firstsurface of the substrate.

In still another example embodiment, the insulating layer mayconformally cover the first surface of the substrate, a bottom surfaceof the trench, and sidewalls of the trench.

In still another example embodiment, the method may further includeforming photoelectric conversion parts in pixel regions of thesubstrate.

According to yet another example embodiment, an image sensor includes asubstrate including pixel regions having a trench there between, and aninsulating pattern in the trench. The insulating pattern includes aninsulating layer on a first surface of the substrate and conformallyformed to surround an air gap. The insulating layer has a firstrefractive index and a first volume, the air gap has a second refractiveindex and a second volume, the first refractive index is higher than thesecond refractive index, and the first volume is lower than the secondvolume.

In yet another example embodiment, a refractive index of the insulatinglayer may be lower than that of the substrate.

In yet another example embodiment, an upper portion of the trench may bedelimited by the insulating layer.

In yet another example embodiment, the insulating layer may extend alonga bottom surface and sidewalls of the trench.

In yet another example embodiment, a thickness of the insulating layeron the first surface of the substrate may be equal to that of theinsulating layer on the bottom surface and the sidewalls of the trench.

In yet another example embodiment, a width of a bottom portion of theinsulating pattern may be narrower than a width of an intermediateportion of the insulating pattern.

In yet another example embodiment, a width of an upper portion of theinsulating pattern may be narrower than a width of an intermediateportion of the insulating pattern.

BRIEF DESCRIPTION OF THE DRAWINGS

The inventive concepts will become more apparent in view of the attacheddrawings and accompanying detailed description.

FIG. 1 is an equivalent circuit diagram illustrating an image sensoraccording to some example embodiments of the inventive concepts;

FIG. 2A is a plan view illustrating an image sensor according to someexample embodiments of the inventive concepts;

FIG. 2B is a cross-sectional view taken along a line I-II of FIG. 2A;

FIGS. 2C and 2D are enlarged views of a portion ‘III’ of FIG. 2A toillustrate some example embodiments of a device isolation pattern;

FIGS. 3A to 3D are cross-sectional views illustrating a method offorming an image sensor according to some example embodiments of theinventive concepts;

FIG. 4 is a cross-sectional view illustrating an image sensor accordingto other example embodiments of the inventive concepts;

FIGS. 5A to 5C are cross-sectional views illustrating an exampleembodiment of a method of forming the image sensor of FIG. 4;

FIG. 6A is a plan view illustrating an image sensor according to stillother example embodiments of the inventive concepts;

FIG. 6B is a cross-sectional view taken along a line IV-V of FIG. 6A;

FIG. 7A is a schematic block diagram illustrating a processor-basedsystem including an image sensor according to some example embodimentsof the inventive concepts; and

FIG. 7B illustrates an electronic device including an image sensoraccording to some example embodiments of the inventive concepts.

DETAILED DESCRIPTION

The inventive concepts will now be described more fully hereinafter withreference to the accompanying drawings, in which example embodiments ofthe inventive concepts are shown. The advantages and features of theinventive concepts and methods of achieving them will be apparent fromthe following example embodiments that will be described in more detailwith reference to the accompanying drawings. It should be noted,however, that the inventive concepts are not limited to the followingexample embodiments, and may be implemented in various forms.Accordingly, the example embodiments are provided only to disclose theinventive concepts and let those skilled in the art know the category ofthe inventive concepts. In the drawings, embodiments of the inventiveconcepts are not limited to the specific examples provided herein andare exaggerated for clarity.

The terminology used herein is for the purpose of describing particularembodiments only and is not intended to limit the inventive concepts. Asused herein, the singular terms “a,” “an” and “the” are intended toinclude the plural forms as well, unless the context clearly indicatesotherwise. As used herein, the term “and/or” includes any and allcombinations of one or more of the associated listed items. It will beunderstood that when an element is referred to as being “connected” or“coupled” to another element, it may be directly connected or coupled tothe other element or intervening elements may be present.

Similarly, it will be understood that when an element such as a layer,region or substrate is referred to as being “on” another element, it canbe directly on the other element or intervening elements may be present.In contrast, the term “directly” means that there are no interveningelements. It will be further understood that the terms “comprises”,“comprising,”, “includes” and/or “including”, when used herein, specifythe presence of stated features, integers, steps, operations, elements,and/or components, but do not preclude the presence or addition of oneor more other features, integers, steps, operations, elements,components, and/or groups thereof.

Additionally, the example embodiments in the detailed description willbe described with sectional views as ideal example views of theinventive concepts. Accordingly, shapes of the example views may bemodified according to manufacturing techniques and/or allowable errors.Therefore, the example embodiments of the inventive concepts are notlimited to the specific shape illustrated in the example views, but mayinclude other shapes that may be created according to manufacturingprocesses. Areas illustrated in the drawings have general properties,and are used to illustrate specific shapes of elements. Thus, thisshould not be construed as limited to the scope of the inventiveconcepts.

It will be also understood that although the terms first, second, thirdetc. may be used herein to describe various elements, these elementsshould not be limited by these terms. These terms are only used todistinguish one element from another element. Thus, a first element insome example embodiments could be termed a second element in otherexample embodiments without departing from the teachings of the presentinventive concepts. Example embodiments of the present inventiveconcepts explained and illustrated herein include their complementarycounterparts. The same reference numerals or the same referencedesignators denote the same elements throughout the specification.

Moreover, example embodiments are described herein with reference tocross-sectional illustrations and/or plane illustrations that areidealized example illustrations. Accordingly, variations from the shapesof the illustrations as a result, for example, of manufacturingtechniques and/or tolerances, are to be expected. Thus, exampleembodiments should not be construed as limited to the shapes of regionsillustrated herein but are to include deviations in shapes that result,for example, from manufacturing. For example, an etching regionillustrated as a rectangle will, typically, have rounded or curvedfeatures. Thus, the regions illustrated in the figures are schematic innature and their shapes are not intended to illustrate the actual shapeof a region of a device and are not intended to limit the scope ofexample embodiments.

Devices and methods of forming devices according to various exampleembodiments described herein may be embodied in microelectronic devicessuch as integrated circuits, wherein a plurality of devices according tovarious example embodiments described herein are integrated in the samemicroelectronic device. Accordingly, the cross-sectional view(s)illustrated herein may be replicated in two different directions, whichneed not be orthogonal, in the microelectronic device. Thus, a plan viewof the microelectronic device that embodies devices according to variousexample embodiments described herein may include a plurality of thedevices in an array and/or in a two-dimensional pattern that is based onthe functionality of the microelectronic device.

The devices according to various example embodiments described hereinmay be interspersed among other devices depending on the functionalityof the microelectronic device. Moreover, microelectronic devicesaccording to various example embodiments described herein may bereplicated in a third direction that may be orthogonal to the twodifferent directions, to provide three-dimensional integrated circuits.

Accordingly, the cross-sectional view(s) illustrated herein providesupport for a plurality of devices according to various exampleembodiments described herein that extend along two different directionsin a plan view and/or in three different directions in a perspectiveview.

FIG. 1 is an equivalent circuit diagram illustrating an image sensoraccording to some example embodiments of the inventive concepts. FIG. 2Ais a plan view illustrating an image sensor according to some exampleembodiments of the inventive concepts.

Referring to FIGS. 1 and 2A, each of unit pixel regions of an imagesensor may include a photoelectric conversion part PD, a transfertransistor Tx, a reset transistor Rx, a source follower transistor Sx,and an access transistor Ax. The transfer transistor Tx, the resettransistor Rx, the source follower transistor Sx, and the accesstransistor Ax may include a transfer gate TG, a rest gate G1, a sourcefollower gate G2, and an access gate G3, respectively. The photoelectricconversion part PD may be a photodiode including an N-type dopant regionand a P-type dopant region. In other example embodiments, thephotoelectric conversion part PD may include a plurality of photodiodesvertically stacked. The transfer gate TG of the transfer transistor Txmay be disposed on a semiconductor substrate or may extend into thesemiconductor substrate. The semiconductor substrate may include asemiconductor epitaxial layer. A drain of the transfer transistor Tx maycorrespond to a floating diffusion region FD. In addition, the floatingdiffusion region FD may also correspond to a source of the resettransistor Rx. The floating diffusion region FD may be electricallyconnected to the source follower gate G2 of the source followertransistor Sx. The source follower transistor Sx and the resettransistor Rx may be connected in series to each other. The sourcefollower transistor Sx may be connected to the access transistor Ax. Thereset transistor Rx, the source follower transistor Rx, and the accesstransistor Ax may be shared by pixels adjacent to each other, and thus,an integration density of the image sensor may be improved.

A method of operating of the image sensor will be described hereinafter.A power voltage VDD may be applied to drains of the reset transistor Rxand the source follower transistor Sx in a condition that light isshielded, so charges remaining in the floating diffusion region FD maybe discharged. Thereafter, if the reset transistor Rx is turned-off andlight is incident on the photoelectric conversion part PD, electron-holepairs may be generated in the photoelectric conversion part PD. Holesmay be moved into and then accumulated in the P-type dopant region, andelectrons may be moved into and then accumulated in the N-type dopantregion. If the transfer transistor Tx is turned-on, charges (e.g.,electrons and holes) may be transferred into and then accumulated in thefloating diffusion region FD. A gate bias of the source followertransistor Sx may be changed in proportion to the amount of the chargesaccumulated in the floating diffusion region FD, and thus, a sourcepotential of the source follower transistor Sx may be changed. At thistime, if the access transistor Ax is turned-on, a signal correspondingto the charges may be sensed through a column line.

As the image sensor is being highly integrated, a size of thephotoelectric conversion part PD may be reduced. Thus, the amount oflight received in the photoelectric conversion part PD may also bereduced. According to embodiments of the inventive concepts, a deviceisolation pattern isolating the pixel regions from each other mayinclude an air gap, and thus, crosstalk between the pixel regions may bereduced or prevented.

FIG. 2A is a plan view illustrating an image sensor according to someexample embodiments of the inventive concepts, and FIG. 2B is across-sectional view taken along a line I-II of FIG. 2A.

Referring to FIGS. 2A and 2B, an image sensor 1 may include a substrate100, a device isolation pattern 200, and photoelectric conversion partsPD. The substrate 100 may have a first surface 100 a and a secondsurface 100 b opposite to each other. The first surface 100 a maycorrespond to a front side of the substrate 100, and the second surface100 b may correspond to a back side of the substrate 100. For example,the substrate 100 may be a semiconductor substrate (e.g., a siliconsubstrate, a germanium substrate, a silicon-germanium substrate, a II-VIgroup compound semiconductor substrate, or a III-V group compoundsemiconductor substrate) or a silicon-on-insulator (SOI) substrate.

The substrate 100 may include a plurality of pixel regions UP. Thedevice isolation pattern 200 may be provided in the substrate 100 todefine the pixel regions UP. For example, the device isolation pattern200 may be provided between the pixel regions UP. As illustrated in FIG.2B, the device isolation pattern 200 may be a deep-trench isolationpattern provided in a trench 250 recessed from the second surface 100 bof the substrate 100. In an example embodiment, the device isolationpattern 200 may be spaced apart from the first surface 100 a of thesubstrate 100. In an example embodiment, the device isolation pattern200 may extend onto the second surface 100 b of the substrate 200 tocover the second surface 100 b.

According to example embodiments, an upper portion 201 of the deviceisolation pattern may be adjacent to the second surface 100 b of thesubstrate 100, and a lower portion 203 of the device isolation pattern200 may be adjacent to the first surface 100 a of the substrate 100. Inthe present specification, an intermediate portion 202 of the deviceisolation pattern 200 may be provided between the upper portion 201 andthe lower portion 203 and may be defined as a portion of the deviceisolation pattern 200 which has the maximum width W2. Heights of theupper, intermediate and lower portions 201, 202 and 203 may be variouslymodified. The device isolation pattern according to the inventiveconcepts will be described in more detail.

FIGS. 2C and 2D are enlarged views of a portion ‘III’ of FIG. 2A toillustrate some example embodiments of a device isolation pattern.

Referring to FIGS. 2B, 2C, and 2D, a width of the upper portion 201 ofthe device isolation pattern 200 may increase as a distance from thesecond surface 100 b of the substrate 100 increases. The width of theupper portion 201 of the device isolation pattern 200 may be narrowerthan that of the intermediate portion 202 of the device isolationpattern 200. For example, a width W1 of the upper portion 201 of thedevice isolation pattern 200 at the same level as the second surface 100b of the substrate 100 may be narrower than the maximum width W2 of thedevice isolation pattern 200. The width W1 of the upper portion 201 ofthe device isolation pattern 200 at the same level as the second surface100 b of the substrate 100 may be in a range of about 30 nm to about 250nm. The maximum width W2 of the intermediate portion 202 of the deviceisolation pattern 200 may be in a range of about 200 nm to about 300 nm.Here, the width of the device isolation pattern 200 may be defined as adistance between both sidewalls 200 s of the device isolation pattern200, and the sidewalls 200 s may be coplanar with sidewalls of thetrench 250 provided with the device isolation pattern 200. In otherwords, the sidewalls 200 s of the device isolation pattern 200 may be incontact with the sidewalls of the trench 250. In addition, the increaseor decrease in the width of the device isolation pattern 200 may notinclude an undesired error which may occur in a manufacturing process. Awidth of the lower portion 203 of the device isolation pattern 200 maydecrease as a distance from a bottom surface 200 b of the deviceisolation pattern 200 decreases. A width W3 of the bottom surface 200 bof the device isolation pattern 200 may be narrower than the maximumwidth W2 of the intermediate portion 202. In some example embodiments,the upper portion 201 of the device isolation pattern 200 may have aconvex cross section toward the second surface 100 b, and the lowerportion 203 of the device isolation pattern 200 may have a convex crosssection toward the first surface 100 a. However, the inventive conceptsare not limited thereto.

The device isolation pattern 200 may include an insulating layer ILprovided on the bottom surface 200 b and the sidewalls 200 s of thedevice isolation pattern 200. The insulating layer IL may also beprovided on the second surface 100 b of the substrate 100, and thus, theupper portion 201 of the device isolation pattern 200 may be delimitedby or closed with the insulating layer IL. The insulating layer IL mayconformally cover the sidewalls 200 s and the bottom surface 200 b ofthe device isolation pattern 200 and the second surface 100 b of thesubstrate 100. The insulating layer IL may have a thickness of about 5nm to about 7 nm. The insulating layer IL disposed on the sidewalls 200s of the device isolation pattern 200 may have a substantially uniformthickness. The thickness of the insulating layer IL disposed on thesecond surface 100 b of the substrate 100 may be substantially equal tothat of the insulating layer IL disposed on the sidewalls 200 s and thebottom surface 200 b of the device isolation pattern 200. In the presentspecification, the substantial equality of the thickness may have atolerance which may not be undesired but may occur in a depositionprocess. The insulating layer IL may include a single-layer or amulti-layer. The insulating layer IL may include a material of which arefractive index is lower than that of the substrate 100. For example,the insulating layer IL may include a silicon-based insulating material(e.g., silicon nitride, silicon oxide, and/or silicon oxynitride) and/ora high-k dielectric material (e.g., hafnium oxide and/or aluminumoxide).

A natural oxide layer 150 may be provided in the substrate 100 adjacentto the insulating layer IL. For example, the natural oxide layer 150 maybe disposed between the substrate 100 and the insulating layer IL andmay be in contact with the insulating layer IL. The natural oxide layer150 may have a thickness of about 1 nm to about 3 nm. In an exampleembodiment, a top surface ILa of the insulating layer IL disposed on thesecond surface 100 b of the substrate 100 may be flat as illustrated inFIG. 2C. For example, the top surface ILa of the insulating layer ILblocking the trench 250 may be disposed at substantially the same levelas the top surface ILa of the insulating layer IL disposed on the secondsurface 100 b of the substrate 100. In another example embodiment, theinsulating layer IL closing a top end of the trench 250 may have atleast one protrusion ILp, as illustrated in FIG. 2D. For example, a topsurface ILa of the insulating layer IL closing the top end of the trench250 may be higher than the top surface ILa of the insulating layer ILdisposed on the second surface 100 b of the substrate 100.

An air gap AG may be provided in the device isolation pattern 200 andmay be surrounded by the insulating layer IL. Inner sidewalls ILb of theinsulating layer IL disposed on the both sidewalls 200 s of the deviceisolation pattern 200 may be spaced apart from each other. A top surfaceILc of the insulating layer IL disposed on the bottom surface 200 b ofthe device isolation pattern 200 may be spaced apart from a bottomsurface ILd of the insulating layer IL provided in the upper portion 201of the device isolation pattern 200. The air gap AG may be provided inthe substrate 100 by the insulating layer IL.

Referring again to FIG. 2B, the refractive index of the device isolationpattern 200 may be lower than that of the substrate 100. In some exampleembodiments, if the substrate 100 has a first refractive index n1 andthe device isolation pattern 200 has a second refractive index n2, thedevice isolation pattern 200 may have a material that satisfies aconditional expression “(n1 Sin θ)/n2>1”. For example, the insulatinglayer IL may include a material that has a refractive index lower thanthat of the substrate 100 and satisfies the total reflection condition.Thus, a crosstalk phenomenon between the pixel regions UP may be reducedor prevented. For example, light may be obliquely incident on one of thepixel regions UP through the second surface 100 b of the substrate 100.In this case, the light may be totally reflected by the device isolationpattern 200, so it may not be incident on neighboring pixel regions UP.

The device isolation pattern 200 may include the air gap AG surroundedby the insulating layer IL, and thus, the crosstalk phenomenon may bereduced. The air gap AG may include a material (e.g., air) of which arefractive index is lower than that of the insulating layer IL. As avolume ratio of the air gap AG to the device isolation pattern 200increases in the substrate 100, a total refractive index of the deviceisolation pattern 200 may decrease. The insulating layer IL may have arelatively thin thickness and may conformally cover the sidewalls 200 sand the bottom surface 200 b of the device isolation pattern 200, andthus, the volume ratio of the air gap AG to the device isolation pattern200 may be increased. As a result, the crosstalk between the pixelregions UP may be more reduced or prevented.

A photoelectric conversion part PD and a well region PW may be disposedin the substrate 100 of each of the pixel regions UP. The photoelectricconversion part PD may be deep from the first surface 100 a of thesubstrate 100. In other words, the photoelectric conversion part PD maybe spaced apart from the first surface 100 a of the substrate 100. Forexample, the photoelectric conversion part PD may be a region doped withN-type dopants. The well region PW may be adjacent to the first surface100 a of the substrate 100. In other words, the well region PW may bedisposed between the first surface 100 a of the substrate 100 and thephotoelectric conversion part PD. For example, the well region PW may bea region doped with P-type dopants. The photoelectric conversion PD andthe well region PW may be in contact with each other to constitute aphotodiode. A floating diffusion region FD may be disposed in each ofthe well regions PW. The floating diffusion region FD may be a regiondoped with dopants, and a conductivity type of the floating diffusionregion FD may be opposite to that of the well region PW. For example,the floating diffusion region FD may be doped with N-type dopants. Atransfer gate TG may be disposed on the first surface 100 a of thesubstrate 100 of each of the pixel regions UP. A gate insulating layer120 may be provided between the transfer gate TG and the substrate 100.

An interconnection structure 300 may be disposed on the first surface100 a of the substrate 100. The interconnection structure 300 mayinclude a plurality of interlayer insulating layers 310 and a pluralityof interconnections 320. One of the interlayer insulating layers 310 maybe in contact with the first surface 100 a of the substrate 100 and maycover the transfer gates TG. A contact 305 may penetrate at least one ofthe interlayer insulating layers 310 so as to be in contact with thefloating diffusion region FD. Unlike FIG. 2B, the interconnectionstructure 300 may be disposed on the second surface 100 b of thesubstrate 100 and may be disposed between the insulating layer IL and ananti-reflection layer 400.

The anti-reflection layer 400 may be disposed on the second surface 100b of the substrate 100 to cover the device isolation pattern 200. Acolor filter 410 and a micro-lens 420 may be disposed on theanti-reflection layer 400 of each of the pixel regions UP. The colorfilters 410 may be arranged in a matrix form to constitute a colorfilter array. In an example embodiment, the color filter array may be aBayer pattern including a red filter, a green filter, and a blue filter.In other example embodiments, the color filter array may include ayellow filter, a magenta filter, and a cyan filter. In addition, thecolor filter array may further include a white filter. A grid pattern405 may be disposed between the color filters 410 on the anti-reflectionlayer 400. In another example embodiment, the grid pattern 405 may beomitted.

FIGS. 3A to 3D are cross-sectional views illustrating a method offorming an image sensor according to some embodiments of the inventiveconcepts. Hereinafter, the descriptions mentioned above will be omittedor mentioned briefly to avoid duplication of explanation.

Referring to FIGS. 3A and 3B, a substrate 100 including a plurality ofpixel regions UP may be prepared. At this time, a first surface 100 a ofthe substrate 100 may face upward unlike FIG. 3A. A plurality of ionimplantation processes may be performed on the first surface 100 a ofthe substrate 100 to form photoelectric conversion parts PD, wellregions PW, and floating diffusion regions FD in substrate 100 of thepixel regions UP, respectively. The substrate 100, the photoelectricconversion parts PD, the well regions PW, and the floating diffusionregions FD may be the same as described with reference to FIGS. 2A and2B. A transfer gate TG may be formed on the first surface 100 a of thesubstrate 100 of each of the pixel regions UP. In another exampleembodiment, the floating diffusion regions FD may be formed after theformation of the transfer gates TG. An interconnection structure 300 maybe formed on the first surface 100 a of the substrate 100. Theinterconnection structure 300 may include interlayer insulating layers310, interconnections 320, and contacts 305. Thereafter, the substrate100 may be overturned, so a second surface 100 b of the substrate 100may face upward.

A mask pattern 500 may be formed on the second surface 100 b of thesubstrate 100. The mask pattern 500 may have an opening 550 having agiven (or alternatively, predetermined) width W4, and the opening 550may expose the second surface 100 b of the substrate 100. The exposedsecond surface 100 b of the substrate 100 may be etched to form a trench250 in the substrate 100. The exposed second surface 100 b may beisotropically etched. In some example embodiments, a process gascontaining fluorine (e.g., a SF₆ gas) may be used during the isotropicetching process. The trench 250 may extend into the substrate 100disposed under the mask pattern 500 by the isotropic etching process. Awidth W1 of the trench 250 at the same level as the second surface 100 bof the substrate 100 may be substantially equal to or greater than thewidth W4 of the opening 550. A width of an upper portion 251 of thetrench 250 may increase as a distance from the second surface 100 bincreases. A shape of a cross section of the trench 250 may correspondto the shape of the cross section of the device isolation pattern 200described with reference to FIGS. 2A and 2B. The intermediate portion252 of the trench 250 may have the maximum width W2 of the trench 250. Awidth of a lower portion 253 of the trench 250 may decrease as adistance from a bottom surface of the trench 250 decreases. A width ofthe bottom surface of the trench 250 may be narrower than a width (e.g.,the maximum width W2) of the intermediate portion 252 of the trench 250.The widths W1, W2 and W3 of the trench 250 illustrated in FIG. 3B may besubstantially equal to the widths W1, W2 and W3 of the device isolationpattern 200 illustrated in FIGS. 2B to 2D, respectively. In an exampleembodiment, the upper portion 251 of the trench 250 may have a crosssection having an upward convex curvature, and the lower portion 253 ofthe trench 250 may have a cross section having a downward convexcurvature. However, the inventive concepts are not limited thereto. Thetrench 250 may be formed between the pixel regions UP in the substrate100. Next, the mask pattern 500 may be removed.

Referring to FIGS. 3B and 3C, an insulating layer IL may be formed onthe second surface 100 b of the substrate 100 and an inner surface ofthe trench 250, and thus, a device isolation pattern 200 including anair gap AG may be formed. The insulating layer IL may be formed of aninsulating material of which a refractive index is lower than that ofthe substrate 100. For example, the insulating layer IL may include thesilicon-based material (e.g., silicon nitride, silicon oxide, and/orsilicon oxynitride) and/or the high-k dielectric material (e.g., hafniumoxide and/or aluminum oxide), as described with reference to FIGS. 2Aand 2B. The insulating layer IL may be formed by an atomic nucleusdeposition method with excellent step coverage and may be deposited onthe second surface 100 b of the substrate 100 and sidewalls and thebottom surface of the trench 250. A top end of the upper portion 251 ofthe trench 250 may be delimited by or closed with the insulating layerIL, so the air gap AG may be formed in the device isolation pattern 200.The device isolation pattern 200 may be formed in the substrate 100 andmay cover the second surface 100 b of the substrate 100. The insulatinglayer IL may have a thickness of about 5 nm to about 7 nm. According toembodiments of the inventive concepts, the width of the upper 251 of thetrench 250 may be narrower than that of the intermediate portion 252 ofthe trench 250, and thus, the trench 250 may be more easily delimited byor closed with the insulating layer ILeven though the insulating layerIL is conformally formed with a relatively thin thickness. In otherwords, the air gap AG may be easily formed in the device isolationpattern 200.

Referring to FIGS. 2C, 2D, and 3C, a natural oxide layer 150 may befurther formed between the substrate 100 and the insulating layer IL.The inner surface of the trench 250 and the second surface 100 b of thesubstrate 100 may be exposed before or during the deposition process ofthe insulating layer IL. The exposed substrate 100 may be oxidized toform the natural oxide layer 150 adjacent to the insulating layer IL.The natural oxide layer 150 may be formed in the substrate 100 adjacentto the inner surface of the trench 250 and the second surface 100 b ofthe substrate 100. The insulating layer IL blocking the top end of thetrench 250 may have the flat top surface illustrated in FIG. 2C or thetop surface including the protrusion illustrated in FIG. 2D.

Referring to FIG. 3D, an anti-reflection layer 400, a grid pattern 405,color filters 410, and micro-lenses 420 may be formed on the secondsurface 100 b of the substrate 100. The anti-reflection layer 400, thegrid pattern 405, the color filters 410, and the micro-lenses 420 may bethe same as described with reference to FIGS. 2A and 2B. The imagesensor 1 may be manufactured by the manufacturing processes describedabove.

FIG. 4 is a cross-sectional view corresponding to the line I-II of FIG.2A to illustrate an image sensor according to other example embodimentsof the inventive concepts.

Referring to FIG. 4, an image sensor 2 may include a substrate 100, adevice isolation pattern 200, and photoelectric conversion parts PD. Aninterconnection structure 300 may be disposed on a first surface 100 aof the substrate 100. The interconnection structure 300 may includeinterlayer insulating layers 310 and interconnections 320. Ananti-reflection layer 400, a grid pattern 405, color filters 410, andmicro-lenses 420 may be disposed on a second surface 100 b of thesubstrate 100. In another example embodiment, unlike FIG. 4, theinterconnection structure 300 may be disposed between theanti-reflection layer 400 and the second surface 100 b of the substrate100.

The substrate 100 may include a plurality of pixel regions UP. A deviceisolation pattern 200 may be provided in the substrate 100 to define thepixel regions UP. The device isolation pattern 200 may be provided in atrench 250 recessed from the first surface 100 a of the substrate 100.The device isolation pattern 200 may extend onto the first surface 100 aof the substrate 100 to cover the first surface 100 a. A bottom surface200 b of the device isolation pattern 200 may be adjacent to the secondsurface 100 b of the substrate 100 but may be spaced apart from thesecond surface 100 b.

In example embodiments, an upper portion 201 of the device isolationpattern 200 may be adjacent to the first surface 100 a of the substrate100, and a lower portion 203 of the device isolation pattern 200 may beadjacent to the second surface 100 b of the substrate 100. The upperportion 201 of the device isolation pattern 200 may have a narrowerwidth than an intermediate portion 202 of the device isolation pattern200. A width of the upper portion 201 may increase as a distance fromthe first surface 100 a of the substrate 100 increases. For example, awidth W1 of the upper portion 201 of the device isolation pattern 200 atthe same level as the first surface 100 a may be in a range of about 30nm to about 250 nm. The intermediate portion 202 of the device isolationpattern 200 may have the maximum width W2 of about 200 nm to about 300nm. A width of the lower portion 203 of the device isolation pattern 200may decrease as a distance from the bottom surface 200 b of the deviceisolation pattern 200 decreases. A width W3 of the bottom surface 200 bof the device isolation pattern 200 may be narrower than the maximumwidth W2 of the intermediate portion 202. In an example embodiment, theupper portion 201 of the device isolation pattern 200 may have a crosssection which is convex toward the first surface 100 a of the substrate100, and the lower portion 203 of the device isolation pattern 200 mayhave a cross section which is convex toward the second surface 100 b ofthe substrate 100. However, the inventive concepts are not limitedthereto.

The device isolation pattern 200 may include an insulating layer ILprovided on the bottom surface 200 b and sidewalls 200 s of the deviceisolation pattern 200. The insulating layer IL may include thesilicon-based material and/or the high-k dielectric material describedwith reference to FIGS. 2A and 2B. The insulating layer IL may also beprovided on the first surface 100 a of the substrate 100, and thus, theupper portion 201 of the device isolation pattern 200 may be delimitedby or closed with the insulating layer IL. The insulating layer IL mayconformally cover the sidewalls 200 s and the bottom surface 200 b ofthe device isolation pattern 200 and the first surface 100 a of thesubstrate 100. The insulating layer IL may have a thickness of about 5nm to about 7 nm. The thickness of the insulating layer IL disposed onthe first surface 100 a of the substrate 100 may be substantially equalto that of the insulating layer IL disposed on the sidewalls 200 s andthe bottom surface 200 b of the device isolation pattern 200. Asdescribed with reference to FIGS. 2C and 2D, the natural oxide layer 150may be provided in the substrate 100 adjacent to the insulating layerIL. In other words, the natural oxide layer 150 may be disposed betweenthe substrate 100 and the insulating layer IL.

An air gap AG may be provided in the device isolation pattern 200between the pixel regions UP of the substrate 100 and may be surroundedby the insulating layer IL. The device isolation pattern 200 may have arefractive index lower than that of the substrate 100. For example, arefractive index of the insulating layer IL may be lower than that ofthe substrate 100, and a refractive index of the air gap AG may be lowerthan that of the insulating layer IL. Since the insulating layer IL isconformally formed with a relatively thin thickness, a volume ratio ofthe air gap AG to the device isolation pattern 200 may be increased. Asa result, crosstalk between the pixel regions UP may be reduced orprevented.

A photoelectric conversion part PD, a well region PW, and a floatingdiffusion region FD may be disposed in the substrate 100 of each of thepixel regions UP. A transfer gate TG may be disposed on the firstsurface 100 a of the substrate 100 of each of the pixel regions UP. Thephotoelectric conversion parts PD, the well regions PW, the floatingdiffusion regions FD, and the transfer gates TG may be the same asdescribed with reference to FIGS. 2A and 2B.

A method of forming the image sensor 2 according to the present exampleembodiment will be described hereinafter.

FIGS. 5A to 5C are cross-sectional views illustrating an exampleembodiment of a method of forming the image sensor of FIG. 4.Hereinafter, the descriptions mentioned above will be omitted ormentioned briefly to avoid duplication of explanation.

Referring to FIGS. 5A and 5B, a substrate 100 including a plurality ofpixel regions UP may be prepared. A photoelectric conversion part PD, awell region PW, and a floating diffusion region FD may be formed insubstrate 100 of each of the pixel regions UP. Unlike FIG. 3B, a maskpattern 500 may be formed on the first surface 100 a of the substrate100 to expose the first surface 100 a. The substrate 100 exposed by themask pattern 500 may be isotropically etched to form a trench 250. Theisotropic etching process may be performed under the same condition asdescribed with reference to FIGS. 3A and 3B. A cross-sectional shape andwidths of the trench 250 may correspond to the cross-sectional shape andthe widths of the device isolation pattern 200 illustrated in FIG. 4. Awidth W1 of an upper portion 251 of the trench 250 at the same level asthe first surface 100 a may be equal to or greater than a width W4 of anopening 550 of the mask pattern 500. A width of the upper portion 251 ofthe trench 250 may increase as a distance from the first surface 100 aincreases. An intermediate portion 252 of the trench 250 may have themaximum width W2 of the trench 250. A width of a lower portion 253 ofthe trench 250 may decrease as a distance from a bottom surface of thetrench 250 decreases. Thereafter, the mask pattern 500 may be removed.

Referring to FIG. 5C, an insulating layer IL may be formed on the firstsurface 100 a of the substrate 100 and an inner surface of the trench250 to form a device isolation pattern 200 including an air gap AG. Theformation process of the insulating layer IL may be performed asdescribed with reference to FIG. 3C. The upper portion 251 of the trench250 may be delimited by or closed with the insulating layer IL, andthus, the air gap AG may be formed on the device isolation pattern 200.The insulating layer IL may have a thickness of about 5 nm to about 7nm. According to embodiments of the inventive concepts, the upperportion 251 of the trench 250 may be narrower than the intermediateportion 252 of the trench 250, so the upper portion 251 of the trench250 may be more easily delimited by or closed with the insulating layerIL. As a result, the air gap AG may be easily formed. A natural oxidelayer 150 may be further formed in the substrate 100 adjacent to theinsulating layer IL.

Referring again to FIG. 4, transfer gates TG and an interconnectionstructure 300 may be formed on the first surface 100 a of the substrate100. The interconnection structure 300 may cover the transfer gates TG.In an example embodiment, the floating diffusion regions FD may beformed after the formation of the transfer gates TG. Next, the substrate100 may be overturned, so the second surface 100 b of the substrate 100may face upward. The anti-reflection layer 400, the grid pattern 405,the color filters 410, and the micro-lenses 420 may be formed on thesecond surface 100 b of the substrate 100 to manufacture the imagesensor 2.

FIG. 6A is a plan view illustrating an image sensor according to stillother example embodiments of the inventive concepts. FIG. 6B is across-sectional view taken along a line IV-V of FIG. 6A.

Referring to FIGS. 6A and 6B, an image sensor 3 may include a substrate100, a device isolation pattern 200, and photoelectric conversion partsPD. A first surface 100 a of the substrate 100 may correspond to a frontside, and a second surface 100 b of the substrate 100 may correspond toa back side. An interconnection structure 300 may be disposed on thefirst surface 100 a of the substrate 100. An anti-reflection layer 400,a grid pattern 405, color filters 410, and micro-lenses 420 may bedisposed on the second surface 100 b of the substrate and may be thesame as described with reference to FIGS. 2A and 2B. Unlike FIGS. 6A and6B, the interconnection structure 300 may be disposed on the secondsurface 100 b of the substrate 100 and may be disposed between aninsulating layer IL and the anti-reflection layer 400.

The photoelectric conversion part PD and a well region PW may bedisposed in the substrate 100 of each of the pixel regions UP. Thephotoelectric conversion part PD may be deep from the first surface 100a of the substrate 100. The photoelectric conversion part PD may be aregion which is doped with N-type dopants in the substrate 100. The wellregion PW may be adjacent to the first surface 100 a of the substrate100 and may be disposed between the first surface 100 a and thephotoelectric conversion part PD. The well region PW may be a regiondoped with P-type dopants. The well region PW and the photoelectricconversion part PD may constitute a photodiode.

A shallow device isolation layer STI may be provided in the well regionPW to define an active region of the transistors Tx, Rx, Ax and Sx. Theshallow device isolation layer STI may be shallower than the deviceisolation pattern 200. In a region, the shallow device isolation layerSTI and the device isolation pattern 200 may vertically overlap witheach other.

A gate insulating layer may be disposed between the substrate 100 and atransfer gate TG. A top surface of the transfer gate TG may be higherthan the first surface 100 a of the substrate 100, and a bottom surfaceof the transfer gate TG may be disposed in the well region PW. Thetransfer gate TG may include a protruding portion TG2 and a buriedportion TG1. The protruding portion TG2 may be disposed on the firstsurface 100 a of the substrate 100 and may be covered by theinterconnection structure 300. The buried portion TG1 may extend intothe substrate 100. A floating diffusion region FD may be disposedbetween one sidewall of the buried portion TG1 and the shallow deviceisolation layer STI in the substrate 100. The floating diffusion regionFD may be a region doped with N-type dopants. The shallow deviceisolation layer STI may further define an additional active regionspaced apart from the active region in each of the pixel regions UP. Theadditional active region may also be spaced apart from the transfer gateTG. A ground dopant region 110 may be disposed in the additional activeregion. The ground dopant region 110 may be dopant with dopants of thesame conductivity type as dopants of the well region PW. For example,the ground dopant region 110 may be doped with P-type dopants. Here, adopant concentration of the ground dopant region 110 may be higher thanthat of the well region PW. The floating diffusion region FU and theground dopant region 110 may be electrically connected tointerconnections 320 through contacts 305.

The substrate 100 may include a plurality of the pixel regions UP. Thedevice isolation pattern 200 may be provided in the substrate 100 todefine the pixel regions UP. The device isolation pattern 200 may be adeep-trench isolation pattern provided in a trench 250 recessed from thesecond surface 100 b of the substrate 100. The device isolation pattern200 may extend onto the second surface 100 b to cover the second surface100 b.

In the present example embodiment, an upper portion 201 of the deviceisolation pattern 200 may be adjacent to the second surface 100 b of thesubstrate 100, and a lower portion 203 of the device isolation pattern200 may be adjacent to the first surface 100 a of the substrate 100. Awidth of the upper portion 201 of the device isolation pattern 200 mayincrease as a distance from the second surface 100 b increases. Theupper portion 201 of the device isolation pattern 200 may be narrowerthan an intermediate portion 202 of the device isolation pattern 200.The intermediate portion 202 of the device isolation pattern 200 mayhave the maximum width W2 of the device isolation pattern 200. A widthof the lower portion 203 of the device isolation pattern 200 maydecrease as a distance from a bottom surface 200 b of the deviceisolation pattern 200 decreases. A width W3 of the bottom surface 200 bof the device isolation pattern 200 may be smaller than the maximumwidth W2 of the intermediate portion 202. In an example embodiment, theupper portion 201 of the device isolation pattern 200 may have a crosssection which is convex toward the second surface 100 b of the substrate100, and the lower portion 203 of the device isolation pattern 200 mayhave a cross section which is convex toward the first surface 100 a ofthe substrate 100. However, the inventive concepts are not limitedthereto.

The device isolation pattern 200 may include an insulating layer ILprovided on the bottom surface 200 b and sidewalls 200 s of the deviceisolation pattern 200. The upper portion 201 of the device isolationpattern 200 may be delimited by or closed with the insulating layer IL.A thickness and a material of the insulating layer IL may be the same asdescribed with reference to FIGS. 2A and 2B. The insulating layer IL mayconformally cover the second surface 100 b of the substrate 100 and thesidewalls 200 s and a bottom surface 200 b of the device isolationpattern 200. The thickness of the insulating layer IL disposed on thesecond surface 100 b of the substrate 100 may be substantially equal tothat of the insulating layer IL disposed on the sidewalls 200 s and thebottom surface 200 b of the device isolation pattern 200. As describedwith reference to FIGS. 2C and 2D, the natural oxide layer 150 may beprovided between the insulating layer IL and the substrate 100.

An air gap AG may be provided in the device isolation pattern 200between the pixel regions UP of the substrate 100 and may be surroundedby the insulating layer IL. The device isolation pattern 200 may have arefractive index lower than that of the substrate 100. For example, arefractive index of the insulating layer IL may be lower than that ofthe substrate 100, and a refractive index of the air gap AG may be lowerthan that of the insulating layer IL. Since the insulating layer IL isconformally formed with a relatively thin thickness, a volume ratio ofthe air gap AG to the device isolation pattern 200 may be increased. Asa result, crosstalk between the pixel regions UP may be reduced orprevented.

As described with reference to FIGS. 3A to 3C, a formation process ofthe device isolation pattern 200 according to the present exampleembodiment may include the process of forming the trench 250 and theprocess of forming the insulating layer IL. Forming the trench 250 mayinclude isotropically etching the substrate 100 exposed by the maskpattern. A cross-sectional shape of the trench 250 may correspond to thecross-sectional shape of the device isolation pattern 200. The shallowdevice isolation layer STI may act as an etch stop layer in the processof forming the trench 250, so a bottom surface of the trench 250 may bein contact with one surface of the shallow device isolation layer STI.In another example embodiment, an etching condition may be adjusted, sothe bottom surface of the trench 250 may be spaced apart from the onesurface of the shallow device isolation layer STI. The insulating layerIL may be formed on the second surface 100 b, and an upper portion ofthe trench 250 may be delimited by or closed with the insulating layerIL. Thus, the device isolation pattern 200 including the air gap AG maybe formed. According to embodiments of the inventive concepts, the upperportion of the trench 250 may be narrower than an intermediate portionof the trench 250, so the upper portion of the trench 250 may be moreeasily delimited by or closed with the insulating layer IL. In otherwords, the air gap AG may be more easily formed.

FIG. 7A is a schematic block diagram illustrating a processor-basedsystem including an image sensor according to example embodiments of theinventive concepts. FIG. 7B illustrates an electronic device includingan image sensor according to example embodiments of the inventiveconcepts. The electronic device may be a digital camera or a mobiledevice.

Referring to FIG. 7A, a processor-based system 1000 may include an imagesensor 1100, a processor 1200, a memory device 1300, a display device1400, and a system bus 1500. As illustrated in FIG. 7A, the image sensor1100 may capture external image information in response to controlsignals of the processor 1200. The processor 1200 may store the capturedimage information into the memory device 1300 through the system bus1500. The processor 1200 may display the image information stored in thememory device 1300 on the display device 1400.

The system 1000 may be a computer system, a camera system, a scanner, amechanized clock system, a navigation system, a video phone, amanagement system, an auto-focus system, a tracking system, a sensingsystem, or an image stabilization system. However, the inventiveconcepts are not limited thereto. If the processor-based system 1000 isapplied to the mobile device, the system 100 may further include abattery used to supply an operating voltage to the mobile device.

FIG. 7B illustrates a mobile phone 2000 implemented with the imagesensor according to example embodiments of the inventive concepts. Inother example embodiments, the image sensor according to exampleembodiments of the inventive concepts may be applied to a smart phone, apersonal digital assistant (PDA), a portable multimedia player (PMP), adigital multimedia broadcast (DMB) device, a global positioning system(GPS) device, a handled gaming console, a portable computer, a webtablet, a wireless phone, a digital music player, a memory card, and/orother electronic products transmitting and/or receiving information bywireless.

According to example embodiments of the inventive concepts, theinsulating layer may be disposed on the top surface of the substrate todelimit or close the upper portion of the trench, so the deviceisolation pattern including the air gap may be formed in the substrate.The width of the trench may decrease as a distance from the top surfaceof the substrate decreases. The upper portion of the trench may benarrower than the intermediate portion of the trench, and thus, theupper portion of the trench may be more easily delimited by or closedwith the insulating layer. As a result, the air gap may be more easilyformed in the device isolation pattern. The insulating layer may beconformally formed with a relatively thin thickness, so the volume ratioof the air gap to the device isolation pattern may be increased. Inother words, the refractive index of the device isolation pattern may bereduced to reduce or prevent the crosstalk between the pixel regions.

While the inventive concepts have been described with reference toexample embodiments, it will be apparent to those skilled in the artthat various changes and modifications may be made without departingfrom the spirits and scopes of the inventive concepts. Therefore, itshould be understood that the above embodiments are not limiting, butillustrative. Thus, the scopes of the inventive concepts are to bedetermined by the broadest permissible interpretation of the followingclaims and their equivalents, and shall not be restricted or limited bythe foregoing description.

What is claimed is:
 1. A method of forming an image sensor, the methodcomprising: forming a trench in a substrate, the trench having anintermediate portion and an upper portion narrower than the intermediateportion; and forming an insulating layer on a first surface of thesubstrate delimiting the upper portion of the trench to form a deviceisolation pattern defining an air gap, the device isolation patterndefining pixel regions in the substrate.
 2. The method of claim 1,wherein the forming a trench comprises: forming a mask pattern having anopening on the first surface of the substrate, the opening having afirst width; and etching the substrate exposed by the mask pattern,wherein the upper portion of the trench has a width equal to or greaterthan the first width.
 3. The method of claim 2, wherein the etchingisotropically etches the substrate using an etching gas containingfluorine.
 4. The method of claim 2, wherein the forming a trench formsthe trench to extend under the mask pattern in the substrate.
 5. Themethod of claim 1, wherein the forming a trench forms the upper portionof the trench to have an increasing width at an increasing distance fromthe first surface of the substrate.
 6. The method of claim 1, whereinthe forming an insulating layer forms the insulating layer toconformally cover the first surface of the substrate, a bottom surfaceof the trench, and sidewalls of the trench.
 7. The method of claim 1,further comprising: forming photoelectric conversion parts in the pixelregions of the substrate.